This invention relates to polymeric flow and impact modifiers for PVC resin, and to PVC compositions. More particularly, the invention relates to graft polyblends prepared by polymerizing acrylate ester monomers or mixtures of acrylate ester monomers and vinyl aromatic monomers in the presence of a rubbery, saturated hydrocarbon polymer substrate, which are useful as modifiers for PVC to impart improved flow and impact properties thereto, and to PVC compositions having improved flow properties.
Polyvinyl chloride (PVC) resins are commonly fabricated from powders or pellets by thermal processes including extrusion and injection molding, during which the particles must be fused into a molten mass. In conventional processing, the fusion and subsequent processing is aided by incorporation of plasticizers. These plasticizers also improve the flow and shear characteristics of the PVC resins by reducing the melt viscosity, thus enhancing the overall processability. Plasticizers, however, are not entirely satisfactory for many purposes inasmuch as they materially reduce the rigidity and heat distortion temperature of the resin when employed in amounts sufficient to improve processability.
A further method for improving processability has been to employ a blend of PVC with a second polymeric resin together with a monomeric plasticizer to compatibilize the blend. The second polymeric resin, for example, may be a block copolymer having both rigid and rubbery segments, such as those disclosed in U.S. Pat. No. 3,801,529. The presence of large amounts of plasticizer in these compositions again reduces rigidity and the heat distortion temperature of the resin. It is desirable, therefore, to provide a processing aid which can be blended with a PVC resin to improve processability of the resin without materially reducing the heat distortion temperature of the product composition.